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DiZNoG writes "This CNN article discusses NASA experimenting with the idea of using Mag-Lev technology to launch payloads into space. Mentioned in the article is that the U.S. Navy is working on the technology for it's aircraft carriers to launch fighters. Unfortunately the NASA project is horribly underfunded ($30,000) for research. Cool technology, let's hope that the Navy research gets us a step closer to not burning all that Oxygen and Hydrogen to get to space...

Although this technology is by far a better way to get payloads into space, all the energy used to create sufficient electricity to do so would make this method of launch just as costly as the previous. Mag/Lev is an excellent suggestion, after we make more breakthroughs in superconductivity and emf it will become a spectacular solution.

Well, I don't think the *cost* of energy (in terms of dollars) really is the issue here. It is the amount of onboard fuel which displaces the amount of cargo you can take into orbit. And since fuel has weight, the more fuel you add, the more fuel you need to achieve orbit. So, earth-based electricity vs. vehicle based fuel really would be a plus.

IIRC, the terminal velocity of a rocket is (to a first approximation) the product of the logarithm of the ratios of the total mass (including fuel) and the payload mass, and the exhaust velocity. This means you nead TONS of fuel to boost a small payload, especially given Earth's escape velocity of 11 km/sec.

The advantage here would be that you dont need to burn fuel to make the fuel move. You dont need to add extra weight to get started. Im not an expert, but i assume that the basic idea would be gather speed (not even necessarily vertically to begin with), and then launch it vertically. It needs to be vertical to escape the drag of the atmosphere as quickly as possible.

I didn't think they launched rockets exactly vertically. To get the orbital speed right, they go off at an angle - possibly after goign straight up for the most dense part of the atmosphere. I suppose for geostationary sattelites they don't need quite the rotation (and they need to go further up). Easier to explain with a picture, but no can do here.

This is why they like to launch from near the equator and always orbit in the same direction as the earth - you get a substantial boost (900 miles an hour according to Monty Python).

Definitely doesn't need to be vertical - you're out of half the atmosphere in 7 miles, out of over 99% of the atmosphere by 50 miles high, and by that point the velocity you need to get to orbit needs to be horizontal, not vertical; you still need some vertical thrust to counteract gravity of course, the main point is there's an optimal thrust/weight ratio beyond the atmosphere that is also associated with a specific curved trajectory, far from vertical...

Indeed, since O2 + 2H2 -> 2H2O an oxy-hydrogen motor doesn't look like harming the environment at all, unless it's the size of Madagascar. The winnage is in leaving the motor and its fuel supply Earthbound.

OTOH since launches don't happen continuously 24x7 the launcher could use solar/wind/tidal input and store it in superconducting accumulators for the next launch. These variable inputs are much more practical for powering rare events than for things like home heating or lighting. Win again.

What the previous poster meant was, that
1 molocule Hydrogen (H2) + 2 of Oxygen (O2) gives
2 of water (H2O).
If Slashdot accepted PRE, SUPER, and SUB tags, this would be a lot clearer.
You are right, it takes a lot of energy to make Hydrogen, but according to Web Elements [webelements.com] the normal approch to making Hydrogen is stream + ( carbon or methene), electrolsys of sulphuric acid (SO4+ goes through a complex system, and releases Oxygen, but is far more conductive that water) is too expensive, but it might be different if you want an oxygen supply as well.
The reactions above produce carbon dioxide, so unless its aneroibic methene, Hydrogen rockets will still produce excess CO2.

Anyway, for space launchs, the rocket must either be self powered, or doing atleast the escape velocity when it leaves the end of the launch-rails, which, for the Earth, is 11km/sec, well above the speed of sound, so unless you lauch from the top of a mountain, there will be too much atmospheric drag for non-self powered lauches.
To determine the escape velocity use this formulae
sqrt(2 * Gc * M / r) (from Astronomy 120 [yale.edu])
Where Gc is 6.6725e-11 kg-1m-1s-4
M is planent's mass 5.9 72e24 kg for Earth
r is distance of launch from planet's centre (6.378e6 m)

Not quite. First you need the energy of electricity to create the seperated hydrogen and Oxygen in the first place. Then you burn the hydrogen and oxygen at take off.
With this new thing, you could skip the second step and use electricity at take off. That leaves the initial energy the same but cuts out the launch H and O consumption.
I am always for converting things to electricity. That minimizes the technology we have left to improve.
In other words we can focus on production technology as opposed to consumption technology.

Touche... The amount of coal to be burned to produce the electricity required may (notice I did say may) offset the environmental savings.Now, if they can use solar energy to fire that baby... That would be the shiznit!

all the energy used to create sufficient electricity to do so would make this method of launch just as costly as the previous

Well, not exactly. In a traditional launch, the initial thrust has to get the mass of the payload PLUS a whole LOT of fuel moving. But as the fuel burns, each pound (or ounce, or whatever unit you want) of fuel adds more actual acceleration than the last pound did, because it has the same thrust but less mass that it has to push. The efficiency of the energy spent can be calculated by taking the integral of how much thrust is produced as the mass it needs to push decreases. As the launch progresses, each ounce of fuel has more effect (in the goal of accelerating the rest of the fuel and the payload) than the previous one did.

In the mag-lev case, the mass of the object being launched starts out MUCH MUCH smaller than in a traditional case, and the entire object stays at that smaller mass. By the time the object has reached its target velocity, (I'm simplifying the math a little here) the total energy spent has been mass(final) times velocity squared, instead of the of integral of the mass(inital to final) times velocity squared (mass and time being our changing variables). It'd make more sense if I could figure a way to show mathematic equations in html;), but if you've had some calculus it should make sense. Much less energy is actually used to get a given amount of mass to a given velocity.

Obviously, it still requires energy, but not nearly the amount of energy for a traditional launch. Likely (at this point in the development of the technology) the mag-lev launch would still require some fuel burn at the end, to get the vehicle from the post-mag-lev velocity to an orbital velocity, and to get it up to the right height, but a lot of energy would already have been saved.

In a nutshell, for emphasis: the vast majority of the energy required to launch something into orbit is used at the beginning of the launch, and mag-lev technology would be able to reduce the initial launch sequence's energy dramatically.

In a nutshell, for emphasis: the vast majority of the energy required to launch something into orbit is used at the beginning of the launch, and mag-lev technology would be able to reduce the initial launch sequence's energy dramatically.

In a nutshell for emphasis: Your analysis, and others repeating the same thing, ignore one simple fact: Mag launching is *very inefficient*. It's unclear that there will be any cost savings, LH2 and LOX are fairly cheap, even reducing their costs by 50% won't affect launch costs much. Just because the energy (fuel) required in the vehicle proper is lower does not mean the total energy requirements in the system are lower.

This is true for the moment, but like most technologies, as more research is done, and the technology hits the market, it will improve.

While that's the way to bet, many technologies run afoul of physical law and simply *can't* improve much further. Nuclear power plants for example. They've gotten bigger, but not all that much more efficient since their introduction. You also have to look at where the gains come from. Auto MPG increases have partly come from technological improvements, partly by vastly decreasing the size and performance of the vehicles. (To the point where even more technology had to be deployed to restore safety.) Also, the high MPG's are in the commuter cars, the rest of the market has not come down near as far, but you don't hear that in the ads.

So, much the same as the horse drawn carriage gave way to the truck

The horse drawn carriage was not replaced by the truck. A wide variety of different kinds of horse drawn vehicles were replaced by a wide variety of internal combustion vehicles.

eventually H2/LOX engines must be replaced with something else,

Why 'must' LH2/LOX engines be replaced? Their clean, cheap (outside of the US) and efficient. The major costs of launch are not the engines or their fuel, it's partially the overall vehicle (but needn't be) and largely the personell costs (but needn't be either). Don't confuse the expensive, difficult way that NASA/the US Goverment does things with the way they could be done. (Vast improvements in cost can be done with few improvements, but they step on political toes, so they are unlikely to happen.)

but it will happen slowly, and may not be a big (if any at all) advantage to start with.

If there is no clear advantage, it won't be replaced. Rockets are launched in the real world, cost real money, and must be considered in the light of real economics. These aren't computers where everyone rushes out to buy the latest thing whether it offers tiny improvements or just more flash. These are expensive assets used to handle expensive assets. Try hanging out on sci.space.policy (Usenet), things don't work like you assume.

NASA/JPL is willing to spend money to look into new possibilities, look at the space gun [nasa.gov].(Link is a bit light, but gives the basic idea)

Um, NASA didn't put any money into the space gun IIRC.. At any rate, the 'space gun' in long abandoned. A gun large enough to be useful required unobtanium for the barrel. A gun small enough to be practical required a projectile that was a fairly large rocket in it's own right, the end result almost no gain, while putting the payload in a very hostile launch enviroment.

Sure, they work, but I can't believe that we have hit the pinnicle of launch propulsion technology

No, we haven't, not even for liquid fuel engines. (No serious research and development on booster class motors has been done for nearly forty years.)

However, the basic principal is still valid, more research and the drive to make the better product to sell will ultimatly drive down the price, and increse effeciency.

Your 'basic principle' is *not valid*. Steam powered locomotive engines reached their peak of efficiency around 1910, yet they grew no cheaper per delivered HP. (In fact they grew more expensive over time as larger units were required to handle heavier traffic while remaining economic.) Steam locomotives were replaced with diesel because the life cycle costs were much cheaper. (While other things were made more difficult.) You make the common slashdot mistake of assuming that all technologies behave like computer/electronic technology, they don't, historically speaking electronics are the abberation, not the rule.

So we agree then, old technology was replaced by new technology.

That depends on how slippery you want to get in defining 'technology', I prefer not to use it in the form used today. (Where even minor implementation updates are called 'new technology', even when they aren't.)

NASA/JPL needs to keep trying now things, or we'll never find something better.

First you need to define what you mean by 'better'. Safer? More reliable? cheaper? All these things and more can be done without new technologies! NASA's problems with safety, reliability, and cost are all due to political and historical causes, not because of some intrinsic property of liquid fuel motors.

I'm wondering how much of the benefits of this is in the acceleration/speed they hope to achieve in a small space, versus the height they want to reach. I'm an idiot on the subject, admittedly (who's an expert, anyhow?), but which is more unrealistic, building an EM rail that reaches near orbit, or trying to accelerate 100s of tons verticaly to reach a high speed? (I'm still going to assume that they'll use rockets to reach orbit, and not 100% rely on the rail for the energy.)

In theory they hope to use this to totally replace rocket launches as it would be

A. Safer
- all equipment on ground easy to maintain and in case of a failed launch or problem the rail would still result in a partial launch - meaning the pilot could presumably guide the plane/wahtever to a landing.
- No need to carry volatile chemicals

B. Cheaper since, once agian, everything is on the ground - no need for throwaway boosters, etc Indeed once you pay for the construction all that is left is electricity and maintence.

C. The plan isn't to accelerate them vertically as the G forces would kill a man to obtain earth orbit you have to have a speed of (I think) 25 Km/Sec which would, in a vertical launch scenario of say a 1000 meter tower, result in way over the 9-10 G's a human can survie. Instead they will be launched off of a gradually ascending slope spanning a couple of kilometers.

However, and this is a big iffy, in all honesty this technology will go nowhere without superconducting materials to use in the rail. Without these existing, or any future, non-superconducting material cannot hope to maintain the power output/magnetic field necassary to propel an object to Earth Orbit or Near Earth Orbit (NEO).

[O]nce you pay for the construction all that is left is electricity and maintence.

The same could be said for New York City. The devil is in the details, my friend. Folks thought the Shuttle would open up cheap access to space, since we'd get to reuse the orbiters. Ha ha.

[To avoid dangerously high acceleration, manned flights] will be launched off of a gradually ascending slope spanning a couple of kilometers.

Sorry, but that's still way too short. To achieve a minimum orbital velocity in a 2-kilometer run, you'd have to accelerate at a little more than 1500 gees. Splat.

Even with a 100-kilometer ramp, you'd be dealing with an average acceleration greater than 31 gees. It appears that, as far as space projects go, this will only ever be useful as an initial-stage boost, or for boosting raw materials into space for orbital construction projects.

Of course, it would still make a nice high-tech catapult for lobbing massive conventional weapons hundreds of miles, but of course no one in the Pentagon is thinking of THAT possibility...

To achieve a minimum orbital velocity in a 2-kilometer run, you'd have to accelerate at a little more than 1500 gees.

Yup. And for a more manageable 10g, you'd need a 315km run to reach geosynchronous velocity. Of course, you'd also burn to a crisp in the atmosphere;-)

The advantage of railgun / rocket sled launches is in getting you some of the way up to orbital velocity, but there's still a good long way to go. Basically, you can't reach orbital velocity while still inside the atmosphere, so you have to carry a bunch of fuel up with you whichever way you cut it.

Here's some handy dandy info for those who want to have a play with the numbers and have forgotten their Newtonian stuff:

Geosynchronous orbit is at 42,245m, which requires an orbital velocity of 7869m/s. Gravity is 9.81m/s^2

What all this boils down to, of course, is that the most expensive part of lift is the lower stages. As you get higher, it gets easier - thus the various investigations into high-altitude burns after being lifted there by jet, balloon, dirigible, and now maglev.

Yes, the previous numbers were off, but it is asymptotic. Certainly a 2 km or even 100 km rail isn't going to get you orbital speed. Not on this planet. But it is going to reduce the amount of expendables you have to burn (which, in turn, lowers your weight and further reduces how much you have to burn, yadda yadda yadda).

It remains to be seen that it's: 1) significantly less expensive, 2) as reliable (hah), and 3) as flexible (one of the key dearths of jet/balloon high altitude release) as current rocket launch systems. If it doesn't meet all three it'll die. If it does meet all three it may still die simply because there are people in charge that refuse to look at alternatives to big rockets.

Of course, it would still make a nice high-tech catapult for lobbing massive conventional weapons hundreds of miles

Hmmmm - I think I'd start to ask questions when I notice my neighbor building a giant maglev rail on a mountain pointing at me. Nothing is so suspicious as somebody constructing a gun that can only point at your head.;-)

A. Safer - all equipment on ground easy to maintain and in case of a failed launch or problem the rail would still result in a partial launch - meaning the pilot could presumably guide the plane/wahtever to a landing.

Maybe, maybe not. What if it tosses it fast enough to come off the rail, but not fast enough to maintain (gliding) flight? No safe landing!

- No need to carry volatile chemicals

Sorry, no. Maglev launched vehicles are going to have to carry significant amounts of fuel to boost themselves into orbit. Otherwise they'll pay an incredible penalty in heat sheilding to overcome the atmospheric heating at launch. (And it will be in different places mostly than that required for reentry, so no saving there.)

B. Cheaper since, once agian, everything is on the ground - no need for throwaway boosters, etc Indeed once you pay for the construction all that is left is electricity and maintence.

Maybe, maybe not. You have to get the launch rate up high enough to amortize the cost.

I forgot to mention the (Critical) point was that maglev should be used for *unmanned* launches. Manned launches would require a very long launch platform (over 100km) while, depending upon the stress's a unmanned launch vehicle could withstand, it could be much shorter (perhaps less than 25km assuming the vehicle could withstand 30-40 g's.

And? 30-40G is 5 to ten times *larger* than current systems. That means heavier boosters and more vehicle and payload weight devoted to structure. Best guess? A net loss compared to current systems.

I would imagine for manned launches they would use the maglev track of about 25km to accelerate the craft to Ramjet/Scramjet speeds greatly reducing the amount of fuel needed to be carried.

Actually, you need *more* fuel as you are adding the weight of the ram/scramjets to the booster. You'll still need rockets to get the last velocity increment (actually over 50% of the velocity) you'll need to get to orbit. The rockets now (under your scheme) have to carry the weight of the ram/scramjets, their supporting structure, and the TPS to protect them. (also do keep in mind that it's very, very unlikely that anyone will allow a pilotless winged vehicle to reenter and land anytime in the near future.

Traditional rockets tend to burn up to one quarter of their overall fuel reserves before they lift the first inches off the ground/out the silo.

Maglev might be able to give these devices a good shove before the rockets kick in and might therefore save substantial amounts of fuel (and fuel saved is weight saved, which then saves even more fuel on the way to orbit).

let's hope that the Navy research gets us a step closer to not burning all that Oxygen and Hydrogen to get to space...

Yes, we must reduce emissions of deadly Dihydrogen Monoxide [dhmo.org]! It's already filling our rivers, streams and oceans, and has been found even in the ice of Antarctica! The time to act is now, people! Before our wells are full of this dangerous chemical!

I think you're missing a very important detail. If the shuttle/ship/whatever doesn't need to carry the fuel necessary to get it into orbit then you've just removed a LOT of added weight. Think of how much weight SRBs add, let alone the liquid fuel tank.
I don't know the exact cost/[pound|kilo] to get something into orbit, however reduced weight means less cost and less energy needed per launch. Seems like a win/win situation to me.

I think you're missing a very important detail -- I was making a joke. But let's go ahead and apply this to the shuttle. Here's how far you have to make your acceleration track in order to reach 7,814 m/sec (minimum orbital velocity) at various G-forces:

Think about how long you watch a shuttle launch, and that it's accelerating for that entire time. It takes a long, long track to pull this off. Better to build short, fast ones and use them for launching construction materials into orbit.

Hmm. Too braindead to do the calculation, but do you get a win if you have a circular track? You can go round that, accelerating away and then either let go (wheeee!) or bank off onto a straightening bit.

Anyone care to do some sums on circumference, centripetel (sp?) force (oooh ooh centrigugal/centripetal flame war please) and other interesting numbers?

Those are interesting calculations. Now try this. If you just want to replace the first stage, then how long does the track need to be? Assume that the launch starts off horizontal, and then bends through an arc to over 45% toward vertical. And that you are replacing only the first stage. How long does the track need to be? How high should you try to go? Would Pikes Peak be a good launch site?

To compensate for drag in the atmosphere you need a muzzle exit velocity aroun 10-11 km/s. You'll still need a rocket on board to circularize your orbit less you come back down into the atmospher on the same parabola that you left. You can use this rocket to help you escape though and leave the the
muzzle at a lower velocity. A 30 km launcher could accelerate cargo to 11 km/sec at 4000 gees, and could accelerate a rocket with people to 1.5 km/sec at 8 gees and save a lot of fuel for the rocket.

Of course, an even better solution is to build your mag lev accelerator into a loop like a particle accelerator... then you can accelerate at whatever rate you want:)

Few people here seem to understand the crucial issue. A couple do, but their posts haven't been modded up... here's another try.

You don't build a magrail to give your spacecraft orbital velocity. Of course that's silly, for the reasons given above. You use it to give you some small PART of your velocity. This is extremely beneficial.

The crucial insight is that each bit of fuel you use for some stage of the flight needs to be lifted be even more fuel in the previous stage. Think backwards from orbit and it will make sense.

Say you have a 100-kilo satellite you want to accelerate at a constant rate for some period of time. For the last second of your flight, you need to burn, say, 10 kilos of fuel. That means the second before that, you need enough fuel to accelerate 110 kilos, 100 Kg of spacecraft plus the 10 Kg of fuel you'll need in the next second. So you'll need 11 kilos of fuel for the second-to-last second of acceleration. The second before that, you need 12.1 kilos. and before that, about 15 kilos. If you know anything about exponentials, you can then imagine how much fuel you need for the FIRST few seconds of the flight.

(This is not actually quite how spacecraft usually work, but it illustrates the general point nicely)

Over 90% of the fuel you are carrying is used just to lift the rest of the fuel that is burned later on, and a huge fraction of it is burned in just the first few seconds. And of course each kilo of fuel you carry requires a larger spacecraft to hold it, which in turn weighs more, which in turn requires even more fuel. So, if you can use a 10km or 100km rail to get your first few seconds of acceleration, you save a huge amount of fuel. This means a smaller spacecraft, which in turn means even LESS fuel carried.

The power burned by the railgun/mass driver/maglev whatever may actually be more expensive in raw form than rocket fuel (i.e. kerosene, in Russian rockets, which is less expensive per joule than electricity. US rockets use liquid hydrogen, which costs a bundle because you have to use vast amounts of electricity to cool it.), but it doesn't exponentially increase in magnitude as you head down the rail, because it's transmitted through wires rather than carried as mass in the spacecraft. Every second, you only need the same amount of electricity you used the previous second.

The same is true of chemical-powered ram and shock cannons, where fuel filling a cylindrical pipe is combusted behind the accelerating spacecraft travelling through the pipe. (not recommended for human payloads).

Furthermore, if your spacecraft has wings, this may give you yet another benefit. The shuttle has wings, but launches straight up, meaning for the ascent they are just dead weight requiring a huge, exponentially-scaled mass of fuel to lift. But on an almost-horizontal launching system, the wings can provide lift, and thereby actually be useful on the ascent stage. This of course is made easier if the vehicle already has significant velocity before it even lights its engines.

This whole system may not be a panacea; I'm skeptical too. But it probably is worth looking into, because it may help and doesn't require any technologies that don't yet exist. (unlike skyhooks/beanstalks or other strangenesses)

oh yeah, that's another thing - once the vehicle gets to a certain speed via maglev, you might actually be able to use ramjet engines, which need to be travelling at supersonic speeds just to be lit. This would save on oxidizer.

However, there's no real reason ramjets can't be used in space launches now. . .

1. it does NOT have to be vertical(watch what the shuttle does soon after launch), so the acceleration can be done over longer distance, so less G's. think rail's in hundreds of miles. Expensive, yes, but less than 100 million per launch of shuttle.

If you're building a horizontal gun and making the end turn up, turning radius gets _worse_, because of the higher muzzle velocity. It goes up as the _square_ of the velocity! You need a tower high enough that you might as well make the whole gun a tower.

Mount Everest is 4.4 km high. If you carve a giant channel in it, so that your gun gracefully curves, you get a maximum muzzle velocity of around 0.66 km/sec. Still very, very low.

If you just run a straight gun up the side of a mountain the size of Mt. Everest, you get a straight gun around 6 km long. At 10 gravities maximum acceleration (as per previous post), this gives you 6e5 J, or a velocity of 0.77 km/sec.

Still not enough to make a worthwhile difference.

Bear in mind also that tilting the gun at an angle, like you would going up the side of a mountain, gives you much more atmosphere to go through on the way up. If you try to turn the craft in the atmosphere, you're still forced to turn slowly, and your acceleration limit will be much lower than for a turning gun barrel, making the turning radius much larger (turning radius is inversely proportional to radial force).

2. even if it did, you could just build it up the side of a tall mountain, and have it curve gently up, which is kinda the most likly solution anyway, as it put you higher in the air, so less air resistance, closer to orbit, that type of thing.

Air resistance effects are negligable if your rocket's cross-sectional mass is much greater than the cross-sectional mass of the atmosphere it'll be plowing through (15 tonnes per square metre), or if it does most of its acceleration outside most of the atmosphere.

For a conventional heavy-payload rocket, both of these conditions are true, and atmosphere resistance doesn't matter.

well, even with that "muzzle velocity" of 7814m/sec, you'll still need supplemental rocket propulsion to keep the craft going at that speed until it clears the atmosphere, and all that drag.

Plus, at low altitudes, 7814m/sec is going to vaporize your vehicle very quickly - unless you add a heat-shield. Obviously, 3112 G's is going to mean an unmanned launch. Even 15 G's is pretty unrealistic. So you have to add a heat shield for launch, when you don't intend to even have a recovery.
That's not an optimal design.

Even in an unmanned vehicle - 3112 G's is pretty unrealistic. We CAN build a vehicle that could withstand it, but it would probably need so much reinforcement that there'd be less room for cargo - plus, your cargo would now have to be engineered to withstand 3112 Gs.

So really, you have to accellerate magnetically to some speed, probably subsonic, enough to get the vehicle airborne, perhaps a few thousand feet, and THEN ignite rockets. At altitude, air friction won't be as bad an obstacle (nor will the sound barrier).

I've read (on slashdot, years ago, so don't quote me on this) that the majority of rocket thrust is spent lofting more rocket fuel up through the lower and much thicker few miles of the atmosphere. Clear that barrier, and there's a significant savings already. You can't do entirely without rockets, nor would it be wise to try.

yes, but it's also at lower speeds, too. I'm making the *very* coarse assumption of speed being roughly the same at a given altitude on takeoff and reentry, even though it's only correct at altitudes of 0 and orbit. Given thismassive shot of speed, there should be more total friction on this type of launch than reentry.

If I remember a while back, I could have sworn I saw some sort of launch system in either a computer animation demonstration or in a game itself.

This idea would be interesting to apply into space as there is very little friction in space to slow things down. Why not make an addon on to the IIS to launch vehicles to Mars or Venus via this launch method? If the track was long enough it could go faster than convention rocketry. And in fact, less fuel would be needed on the vehicle since the mag-lev was the device that launched it.

The article mentions that you can use a mag-lev system to vastly increase the velocity of an aircraft. But on a carrier, it's also necessary to slow the aircraft down very quickly for a landing. Mag-lev is suited to this task as well - by turning the magnets "backwards," it is possible to reverse the direction of the track.

By using mag-lev for both takeoffs and landings, the Navy could presumably have takeoffs and landings on the same boat very close to each other, without the complexity of the current mechanical system. But, of course, mag-levs are useless for landings from spacee, since spacecraft usually don't have wings - and those that do can just use parachutes for losing speed.

Funny you should mention that...
An American scientist during the 80s (I can't remember his name, but there have been shows about him and his work on Discovery and TLC) thought about creating a massive artillery piece for launching satellites into orbit. The artillery "barrel" would be almost half a mile long, and it would be a large facility. The US wasn't interested in it, and the scientist, very interested in promoting the tech, went to other countries to promote it. Eventually ended up in Iraq selling the tech to Saddam, where it actually started getting built. It was one of the "weapons of mass destruction" destroyed during the gulf war.

I don't think the idea was ever put into actual practice, but if you can lob a several ton shell across countries, you might be able to change the trajectory such that the satellite cuts through the ionisphere (sp?) and can obtain a stable orbit.

I believe you are refering to Gerrald Bull (sp?). He was a Canadian who was murdered in Belgium IIRC. The rumours at the time pointed very heavily towards the Mossad and much less so at the CIA. Check out the following for more info:

An American scientist during the 80s (I can't remember his name, but there have been shows about him and his work on Discovery and TLC) thought about creating a massive artillery piece for launching satellites into orbit.

Turns out that the gun required to launch a useful payload required barrels made from unobtanium and quite long. By the time you added boosters to the payload to cut down on gun size, and move it into something buildable, you didn't save any money and created a very payload hostile launch enviroment. (I.E. pointless)

Pounds (of force and mass) are great units for working with rocket equations because you can "cheat" on your units and use specific impulse (measured in seconds... sort of) instead of using exhaust velocity. I also find it makes it easier to use gees as your unit of accel. than using m/s^2 with kg of mass and newtons of force.

Metric is great fun for calculating electrical problems (IMHO), but English is better for rocketry. In adv. physics, just pick whatever strange units (like measuring velocity in %c) make the equations come out easy then convert back when you are done. Units of measure are just a tool, no need to be a zealot about them.

I'm either 5'11" (say, roughly 6') tall or 180.34cm. Now, which of those gives you a better mental picture of how tall I am? For scientific things, yes, powers of 10 work out real nice and all, but for everyday things, who the heck cares if you have to remember there's 12 inches in a foot... not that hard! The English units make a LOT more sense in everyday sorts of things.

I'm convinced that the ONLY reason "English" units make sense to you is because of your environment. I was always told my height in feet and weight in pounds, but my brother started through the Canadian school system 8 years after me, now that metric has become more pervasive. To him, measuring common distances in metres makes sense.

The only way to make a standard system of weights and measures intuitive to the common person is to make it ubiquitous. Scientific agencies like NASA should be leading the way. So, yes, it really should be dollars per kilogram.

And why the HECK have Star Trek producers ALWAYS used the incorrect pronunciation of kilometre?!? The same as any metric prefix like KILO-gram: it's KILO-metre, NOT kuh-LOM-etre!!! ARGH! That's one of my biggest pet peeves. Imagine saying kuh-LO-gram or cen-TIMI-tre!

you're probably right that it's what you're used to, but my point is that the arbitrary English units are plenty fine, thank you. The primary benefit of metric is that everything converts nicely. Granted. I don't have a need to go converting inches to furlongs everyday, and if I do, I'm sure I can find the conversion rate somewhere.

I guess it's just an American independence thing then... we don't want the French telling us what system of measurement to use.:)

As far as KILO-meter (or metre, for you French) vs ki-LOM-eter, I guess it just sounds better. Probably related to spe-DOM-eter rather than SPEED-O-meter.;) (o-DOM-eter, not O-DO-meter) Actually, since ki-LOM-eters come from France, and many accents in French are on the second syllable, I guess is makes sense! Parle vous FranCAISE? (sorry for the missing accent marks, and stuff...)

> I'm either 5'11" (say, roughly 6') tall or 180.34cm. Now, which of those gives you a better mental picture of how tall I am?

The one you are more used to of course. That doesn't make it better in any objective sense.

I'm about 190cm (say, a handswidth under 2m), or 0.009 furlongs, or 0.3 rods, or 0.09 chains. Which of those gives a better mental picture?

Incidentally are you really 5'11" to within 1/200th of an inch? If not, the apparent accuracy of the ".34" you quote is completely bogus.

> Does metric even have "dry volume" measurements?

Yes of course. Cubic metres. Same as wet volume, since a volume doesn't actually change depending whether its contents are wet or dry. The dimensions of volume are length^3, so the SI unit for volume is (unit for length)^3.

Funny, I actually had this conversation with my fiancee night before last (thanks to Junkyard Wars torpedo episode talking about 50 kg displacing 50 L of water).

The reality is that the English units make more sense to you and I simply because that's what we've been raised with. They are no more or less sensical than metric units. Yes, I'm more comfortable with arbitrary measurements in the English system - I know my handspan is 10". I know one of my knuckles is roughly 1". I know how far a mile is, how big a gallon is, and how heavy 10 pounds is.

But to say that 1 kilometer, or 1 liter, or 1 kilogram is obviously not as simple to understand just shows how short sighted you are. If you'd been raised in a country that had transitioned to these measurements decades ago then you'd be wondering what the hell is up with these silly english units.

And yes, the only time it really matters is when you start doing conversions. You don't have to do them? That's nice. Not planning on doing much cooking are you? Because scaling recipes would sure as hell be easier to do with metric than English. Or doing reasonable conversions in any kind of construction (length of wood, sq ft->sq yd vs sq meter, etc). And I'm not even going to get into doing scientific calculations.

Oh, and before someone whines that metric doesn't make sense unless you convert to a metric time system, get a clue. The time system already has a fairly consistant base - base 60. There isn't a single English system that has anything even vaguely consistent. Besides which, once you get to seconds everyone starts using them as a metric baseline - milliseconds, nanoseconds, megaseconds, etc.

As a counterpoint, however, I do wish people would stop bringing up inane English units like bushel, league, hectares, etc. These units aren't used in anything but the same specialized fields that they were originally invented for. The only units that are in common usage are inches, feet, yards, miles (length); ounces, pounds, tons (weight); and teaspoons, tablespoons, ounces, cups, pints, quarts, gallons (volume - yes, this is the single most fucked up system of the bunch).

The point is that I have no need to figure--in my head--that if you run me through a blender (which I suspect you'd like to do right now) that I'd fit into a typical milk crate. Actually, I'd probably run out a bit...

I know it's X miles from town A to town B. Fine, I have no need to know that in feet, furlongs, nautical miles or ki-LOM-eters:). If I do, the conversions are easy enough.

I know that, rounded to the nearest foot, I'm 6' tall. Closer than you'll get rounding to the nearest meter. Again, no need to convert to inches, hands or miles.

I know that my toilet uses (or is supposed to use) 1.2 gallons per flush. No need to convert to teaspoons, pints, quarts (though that's pretty obvious...) or liters (though that's also stated on the label).

I don't know right off the top of my head the mean distance from earth to the sun in miles or kilometers, but I do know that it is 1 AU, which seems to fit the English system of making the units fit the world rather than the other way around. Oh, I just did the conversion of 1AU to miles and km. 9.300e+7 miles or 1.496e+8 km. I have no need to know this in inches, furlongs, nautical miles, or light-years.

Made my point, right? English measurements are size appropriately to the things measured. There is normally no need to convert between said measures, and if needed, it is easily accomplished.

How come selecting a unit of measure is somehow a government problem? This is a free country. There is nothing to stop you from doing all your measuring and calculating in metric units, if you like them so much. Gov't agenicies, like NASA, generally want all their units to at least end up in metric if you do any contracting for them (how you get them there is usually your own problem). What more would you want? Should we throw engineers in jail who don't "get with the program" and think in metric? Mandate that any manufactured product that is not evenly divisible in millimeters be confiscated and destroyed? If I want to measure all my stuff relative to some long dead monarch's body parts (or even my own body parts, for that matter) then that is my own #@&^ business. Units of measure are a tool, not a religion. There is no reason we HAVE to limit ourselves to just one system. Often using "strange" units can make your equations much easier (eg. measuring accel. in gees instead of m/s^2).

BTW, the "metric to english conversion error" that cost us the mars probe was just one small symptom of a sick management program. Unit conversion alone (either within or between systems) should not pose that big of a technical hurdle for a group like JPL. #@!!, it shouldn't even pose that big a problem to freshman engineering students.

As for metric being easier, now that I own one of these new, cool pocket-sized calculating engines that Messrs. Hewlett and Packard make I can just as easily convert between feet and miles as between centimeters and kilometers. Pick one up yourself, they are a great invention.

"My results seem to be off from what I expected by about a factor of 10. I must have a metric conversion error in... well... somewhere."

Because if you and I are using a different definition of an ounce (or a gram), commerce gets all fscked up [nist.gov]. Setting standards for weights and measures has been a basic government function for centuries; the power to "fix the standard of weights and measures" is an enumerated power of Congress in the U.S. constitution (Article I, section 8) [cornell.edu]; part of that is decreeing what set of units is standard.

I did not ask if DEFINING a unit of measure was a gov't problem (which it admittedly is), I asked if SELECTING one was.

I wasn't suggesting that we could all run around with different definitions of a kilogram or troy ounces, but I was suggesting that it is not the gov'ts business to tell me when to use one or the other in my own calculations or private transactions. Of course, the gov't can and does specify units (usually metric) when you do business with them, but that is perfectly understandable.

The previous poster seemed to think that the President Reagan should have some how shoved the use of metric units down the public's throat under penalty of death or imprisonment (isn't all law ultimately based on one of those threats?). I agree that misrepresenting a unit of measure should be a crime, but I really don't think that using a "non government approved unit of measure" should be one. That seems just a little to draconian for me. If I want to think in feet and pounds then that is my decision. If I want to buy 10 fathoms of rope (and can find a rope-seller that knows what a fathom is), then why can't I?

If I have equipment that makes ¼-20 bolts, and my customers want to buy them then what business is it of the President's? Sure, because they aren't metric bolts I may have problems selling them overseas, but if I don't want to export my bolts then I don't care. If the metric bolt market is profitable enough for me to justify the capital expense of new metric based equipment, then I'll buy one and start making metric bolts. But often the capital cost to retool my business to a new unit of measure cannot be justified (see story below). The gov't could put a gun to my head and make me do it. But telling me that it is "for the good of the country" because some pointy-headed academics think it would be cool if we all used the metric system will not magically change the economics of the situation. If it is profitable then the businessmen will do it without coercion... or they will be put out of business by people who will. There is no reason for the gov't to spend billions of dollars brainwashing the entire population into believing that there is only one true system of measurement (and causing huge economic and technical losses as a result) just so a few anal retentive people can feel comforted by the fact that there are now more "nice round numbers" in the world. They would be horrified by a physicist friend of mine who regularly invents his own units so that he could make parts of his equations cancel out or go to zero (and he would then convert back into "regular" units at the end of the calculation).

A brief little aside: All Air Force transports are built with a certain minimum height for the cargo bay area. That minimum height is the height of a knight on horseback, including his helmet. Of course that is not how it is written in the RFP; it is no doubt given in meters or centimeters (because the gov't is trying to encourage metric use)... but fundamentally the unit is "one mounted knight, including helmet." Just like when I see a blueprint in metric units that calls for a measurement of 25.4mm, I know that the real unit that the part was designed to was 1 inch and it was then converted to metric (probably because the customer wanted it that way). Why use such an archaic standard for aircraft cargo areas? Because the cargo areas have to carry U.S. Army vehicles, and those vehicles are usually designed to be shorter than a mounted knight. They are designed that way because they have to be able to pass under bridges in Europe, some of which date back to the Middle Ages. (I'm sure you can see where this is going) The monarchs ruling Europe back then didn't want to have their knights to have to take off their helmet when they went under bridges (because they would be more vulnerable to attack then) so they decreed that all bridges would be built tall enough to permit a fully armored knight to be able to ride underneath it without having to remove their helmets (I'm sure they used some primitive form of a 95th percentile knight, which probably means that there were one or two tall fellows who occasionally hit their head or had to lean over really far). So, modern aircraft are built to an ancient standard because it is cheaper to design the aircraft and tanks to the old standard than to get all the nations of Europe to rebuild their bridges to some nice round metric height like 10 meters. And that is the right decision... even if it screws horribly with the "nice round number utopia" that some people like to fantasize about.

Based on what I've read so far, it really isn't realistic to expect something like the space shuttle to be placed into orbit 100% from an EM rail. However, I'd go back to those other unconventional designs, like a helicopter or a jet being used as a launch vehicle for something designed to go into orbit. Those are being pushed because the benefit is that they clear the lower, dense atmosphere, which is where a lot of fuel is said to be spent.

If you look at am EM rail as something not to completely launch a vehicle into orbit, but to clear the dense portion of the lower atmosphere (and maybe give it enough velocity to save fuel on acceleration), doesn't it make more sense? That is, an EM rail as part of a greater delivery system, and not the whole delivery system?

Hopefully, we can reduce the weight of the fuel and oxidizer that's needed to be carried on board the vehicle and that will decrease the size of the vehicle," said NASA scientist Kenneth House. "So hopefully, we could get more payload into space with less of the fuel."

They want to reduce the fuel needed. Meaning the launch vehicles will have to do some thrust by themselves, but not nearly as much.

Also, some people have noted that g-forces would be a problem. Not likely, if we angle the vehicle at a 45-degree starting angle we drastically reduce the ammount of g-forces needed.

Another point, the maglev system is frictionless. The LV is at no time during the launch touching the track. You've seen bullet-trains, right? Same consept. This further reduces the work needed to launch a vehicle.

I do see this system working. It will probably be 10 years or so, but it will work.

The article clearly indicates that the maglev is going to provide an initial boost, not the full velocity required to reach orbit. Given that rockets use a large portion of their fuel before clearing the tower (a quarter/half of their fuel, something like that), it would be beneficial to use a maglev to get the craft moving before kicking in the rocket. I would envision they would go a step further and combine it with a scram jet. The scram jet won't work until it's super-sonic, so why not launch it super-sonic from the maglev, kick in the scram jet to the edge of the atmosphere, and then finally open up the liquid oxygen. Seems to me they'd save a tremendous amount of weight. You'd still save a lot of weight even if you leave out the scram jet.

We wouldn't want all the resulting water vapor polluting our atmosphere, and our poor mother earth.

Little known fact: H20 is a greenhouse gas. It's not nearly as bad as CO2, but it can contribute to warming the planet. Of course, I seriously doubt that shuttle launches contribute materially to any kind of warming. We don't launch them very often, and the atmosphere is big. It's just that the idea of "water-vapor pollution" might not be as far-fetched as you make it out to be.

On the other hand, lots of water vapor should also cause more cloud formation, which raises the albedo and should lower the average temperature. There are days that I think that climate science is even more dismal than economics...

I did know that particular fact... and I agree, there isn't much a shuttle launch adds, considering all the power plants out there that dump their steam right into the atmosphere right after it goes through the turbines.

My uncle was a NASA engineer who built devices to study the ozone layer and the greenhouse effect. His team's opinions were a bit different than the doomsayers regarding the greenhouse effect. Mainly, that the Earth cycles through periods of greenhousing followed by glaciation, and that we are on a warming trend anyway.

The amount of greenhouse gases emitted by humans is comparatively low compared to some natural sources like volcanic eruptions.

Interestingly enough, the Mt. Pinnatubo eruption in the early '90s (was 91 or 92,..) spilled more CO2 into the air than people could imagine, but the dust it spilled into the air lowered the average temperature of the northern hemisphere about.5 degrees for almost a year.

It was very noticable, too. We had snow in August, which is normally our hottest month here. (Normally hits near 100 degrees.) There was basically no summer that year.

If lowering the Earth's temperature by.5 degrees has that effect, I would welcome a few more degrees increase! I'd like the safety margin. I really hate the cold!

This makes me feel REALLY old, but the EML technology research has been going on for over 20 years. I recall the 1990 High School CX debate topic very well and spent most of the year debating EML launchers (prototyped on Sandia National Labs railgun). We spent the summer in the library in New Mexico visiting Sandia and UNM to research our cases. They were already launching coffee can-sized payloads at that time.

Some of the EML experiments from the late 80s and early 90s were visited at a 95 IEEE pulsed power conference: here [navy.mil]. Of course, it's been a HOT topic since pre-85, when the first IEEE pulsed power conference was held.

We've been at the brink of maglev space launches for the alst 20 decades. Maybe it'll happen tomorrow. Probably not. There's basically no money in this sort of solution for defense contractors, so it generally languishes in congressional committees when it comes time to fund...

Oh well. It would be cheaper, cleaner, safer, and a whole helluva lot more fun at parties... but the same issues applied 20 years ago as today: it doesn't get funded b/c it's a public works-type solution to space. There's no money for Lockheed in something like that.

Remember - in 2001 - A space yawdezze (book, not movie), Clarke predicted (or at least for literary purposes), that by 1999 we would be using Magnetic Launching. Remember - Floyd was impressed that they were using the power of an entire nuclear bomb's energy output simply to launch him into space. I forget how long clarke speculated the track would have to be, but he was only going to the space station.

What we need now are some nice scifi devices such as Inertial Dampeners, Transporters, and bigass klingon battle cruisers.

We've been at the brink of maglev space launches for the alst 20 decades.

And for pretty much the same reasons as we've been on the brink of fusion power for about the same length of time... Mainly that there are enourmous practical engineering and economic problems between viewgraphs and working hardware. It's not entirely clear that any money will be saved in the near (10-15 yrs) term between the current systems and a maglev system.

The bulk of our current infrastructure has long since been amortized; to replace it with a new system will be tremendously expensive. (Hence the focus of CATS on minimizing infrastructure requirements.) Hardware costs are (mistakenly) believed to dominate launch costs, but the real cost in current generation systems is in payroll. (Again most CATS efforts seek to minimize the costs of preparing the vehicle (ELV) or turn around (RLV).) The trick to reducing space access costs is to reduce life cycle costs, and maglev does just the opposite by introducing a enormous R&D and capital construction costs right at the front end, especially if not accompnied by changes to other parts of the overall system.

a payload the size of most smaller sattelites or even a resupply module for the ISS could easily be flung into space with a railgun. The technology is proven, doesnt require special superconductors, and they have plenty of linear space at the cape to build a launch facility. The only thing they would need is a massive amount of electrical energy... like their own power plant.

In fact they were going to build such a launch system back in the 80's... I remember seeing it in a Pop-Sci magazine when I was in highschool.

Give the spacecraft a push, so you can wait until a certain hight before you turn on the rockets.

This is great if the rockets then actually ignite.
Otherwise you would look kind of silly just throwing a spacecraft high into the air and then just watching as it drops:-)

By the way - to all those posts discussing geo-stationary orbit and earth escape velocity.
You dont need to go all that way:-)
The space station is orbiting in approximately 400
km, and it is much cheaper to go there.

A manned shuttle would have wings, and would be able to glide or power back to a landing strip. Or, if it were a vertical lander, it could do a really fancy tail swing maneuver and touch down with rockets on.

An unmanned wingless craft could be permitted to go splash in the ocean.

That's one of the advantages of conventional launches with liquid-fueled engines. You can start and test the engines for proper operation before you commit to a launch by releasing clamps or blowing bolts to release the launch vehicle from the pad.

Pardon my naivety but if a speed of over 7000 metres/sec is needed to achieve orbit, wouldn't the craft burn up?
And wouldn't it have to be going much faster than that off the launch track in order to be at 7000 m/s as it leaves the atmosphere?
It would be better to use the maglev to achieve the velocity necessary to cause a ramjet (or is it scram?) to ignite so as not to require the assistance of conventional jets, rockets and B52s to launch them.

Imagine a cable running from the top of a 50 km tower into geo-stationary Earth orbit. Travelling on the cable is made through electromagnetic propulsion. Nasa is considering a 50 years timeframe for the space elevator [nasa.gov] to become real.

There are more people looking at this for space launch than just a handful
of guys in Huntsville launching model airplanes. And a lot more than
$30,000 is being spent on it. These guys just did a little better PR
(perhaps the fact that Huntsville is a short drive from CNN's facilities
in Atlanta helped). Surely you don't expect CNN to have the latest
(or even accurate) aerospace news, do you? Do they do an accurate job
reporting about software? Go spend the money on (or find a library
that has) a subscription to Aviation Leak and Space Technology, Janes, or
better yet Journal of Spacecraft and Rockets if you really want to know what
is happening.

Magic Mountain, in Valencia, California. I believe it is the Superman ride. It launches a pretty massive set of roller coaster cars from 0 to 100mph at about 2 Gs. I'm not sure why the designers chose this method, but it is a great proof of concept.

To me, the best use of this kind of launcher would be to get an orbiter up to ramjet speeds, say 500 mph, then let it fly on ramjet power up to a tanker. I'd have the ship fully fueled with LOX, but with almost empty fuel tanks, so that it could be lighter and easier to get off the ground. Once fully fueled, use the ramjet to get to 100,000 ft and Mach 3 or so. From that altitude and speed, single-stage-to-orbit is remarkably easier than it is from the ground. You can use full-expansion engine bells to get good specific impulse, and going from Mach 3 to Mach 25 is significantly delta-V than 0 to Mach 25.

Yes, NASA is always chronically underfunded for it's intended missions, but fortunately they aren't the only ones working on it. The military invests a lot of money in R&D, including pretty far-out projects (thanks to DARPA), and there's a long, long list of technology transfers. So if the Navy develops this one for carriers, it won't be long before someone applies it to space.

Here's some simple physics to show why this idea is great. If a force acts between two bodies, one of mass M1 (the spacecraft) and one of mass M2 (the exhaust gas, or in this case, the earth and launcher), then the energy efficiency of the process is M2 / (M1 + M2). In other words, the more massive the launcher, the more efficient the launch. (For physicists in the audience, I will get into detail if you wish.)

Consider a gas-exhaust rocket. Say that the rocket has a mass of 1000 kg and the fuel has a total mass of 100 kg (don't know if it's realistic, just an example). The efficiency of this process (neglecting heat losses) is 100 / (1000 + 100) = 0.091 = 9.1%. Now, consider the earth/launcher system, with enormous mass compared to the spacecraft. The efficiency of this process is M2 / (M1 + M2) where M2 is a huge number compared to M1. This efficiency is close to 1, or 100%!

What this means is that the vast majority of the energy you put in ends up accelerating the craft. This is opposed to the gas-exhaust system where only 9% of the energy goes into the spacecraft -- the remainder is carried away in the exhaust kinetic energy.

If we ever hope to build large space stations, then cutting the cost of earth launch to $1,000 per pound won't cut it. On the other hand, this technology on the Moon, perhaps with solar cells providing the electrical power, would allow for very cheap transfer of lunar material, refined or not, to points earthward. That could be Earth orbit or L4 or L5.

My father is the John Cole quoted in the CNN article and it's his office that is managing the maglev (among a lot of much more interesting projects), so I am familiar with this particular project.
No one at NASA want's to use maglev as the only method for putting anything into orbit, but rather as a launch assist for chemical rockets. You would be amazed at the weight savings just by accelerating a rocket to 500MPH before using onboard fuel.
Also, another point missed by most is that while maglev has been around a while, one of the main problems has been power availablity. For an operational system, you will need 3-6 Megawatt's in 6 seconds. To solve that problem (they don't think they could get a large nuclear power plant just for this thing) they are thinking about using VERY large flywheels to slowly spin up and store the energy until launch.
And funding is next to nill. The army was kind enough to donate a few model airplains for the test rig. I used to have some MPEG's of this, if I find the URL, I'll post them.
For further perusing and some nice pics, try http://std.msfc.nasa.gov/ast/abstracts/0B_Cole.htm l
and http://std.msfc.nasa.gov/ast/index.html
John Cole Jr.

Except there's that funny problem about space. If you launch a spacecraft off of the ISS with a magnetic launcher, then the ISS itself is moved in the opposite direction (based on the relative mass of the station to the vehicle). That is, the ISS is launched, most likely to a lesser degree though, than the vehicle is. Kind of like (but not really at all like) dropping sandbags from a hot air balloon.

You'd be launching the probe on a tangent to the orbit, not on a perpendicular to the orbit. This would cause the ISS to accelerate along the tangent to the orbit, giving it a higher velocity. You achieve higher orbit by going faster, not by going away from the orbited mass.

Lots of counterintuitive things happen in orbit. For example, if you are chasing a probe and accelerate toward it, it will move farther away - you accelerate, you go into a higher orbit, and your orbital period decreases, so you aren't going around as fast. The probe's orbital period stays the same, so it's now going around faster than you.

Lots of reasons. First problem is to keep the ISS from being flung in the opposite direction of the direction of the launch. You could possibly solve that one by making each launch fire the actual launch vehicle and a waste mass in the opposite direction to conserve momentum, but then you double the power requirements and the mass you have to get into orbit.

The next problem is that because of tidal forces any long linear object in orbit will be pulled into an orientation where the long axis of the station is pointed directly at the earth. The center of mass of any object in orbit at orbital speed, but anything closer to the earth is moving slower than orbital speed (because speed to maintain orbit gets faster the closer you get to the center of the earth, but the whole object can only go at a fixed speed) and anything further away from the center of mass of the station is moving faster than orbital velocity.

At any rate, if you've got a long structure in orbit, one end will point at the earth, the other directly away. The amount of energy required to point the launcher anywhere remotely useful would probably be better spent attached to the object you want to launch in the first place.

Launching that way makes you only cause large amounts of impact craters. something we are really good at putting on mars. How are you going to decelerate? if you launc, in space, with much more energy than you can overcome with the device it's self you will never stop until impact. Atmospheric breaking works only at slower speeds, the speed you are talking about would probably cause impact damage upon hitting the atmosphere of mars.

But why not have a rocket take off that drags a string behind it? And, say, take the string to the moon.

I'm not positive, but I'm pretty sure that no material has the tensile strength to hold its own weight all the way to the moon. If you held a 5 foot string, it weighs practically nothing. If you dug a 100 mile hold and held a 100 mile string that was dangling down it it would rip your arm off. If you suspended it from something stronger than you, the string would just break under its own weight.

Plus you can't anchor a string to the earth and the moon. The earth rotates much faster than the moon orbits. If you attached it to just the earth it would only line up with the moon once a day, and it would be going so fast as it passed it you would be smashed into the moon. By the same token if you attached it to the moon, it would fly around the earth every 24 hours, meaning it would be blazingly fast, about 350 mph. Bad rope burn if you try to grab it.

However, it might be possible to build a 'string' that is strong enough to simply lead into orbit. Anchor one end to the earth, and the other to a large mass slightly outside geosync orbit, which is still way way closer than the moon. Then you can climb the string all the way to the mass and be flung away from the earth. At any rate we still don't have strong enough string. Yet.

Kim Stanley Robinson wrote the RGB Mars book series, in which a space elevator was built on Mars. If I remember correctly (it's been a while since I read it), they modified the orbit of Deimos (or Phobos, I forget which) to geosynchronous, grabbed an asteroid or two from the asteroid belt, and had self-replicating robots build a factory there and start "spinning" diamond-filament threads.

By the time the asteroid got to Mars, most of the cable was already built, at which point it was anchored at a massive hold on the surface, and elevator cars were constructed to go up and down the elevator, using counterweights.

I believe that the problem of balancing it if you tried to "launch" something off the top of the platform was to simply give it a little push away, let it float off on it's own, and then use it's own engines to propel it.

Although it may seem a bit farfetched, I think that within the next decade, technology will allow us to realistically dream of doing this, although since we don't have nice-sized moons like Deimos or Phobos, we'd need to bring a bunch of asteroids in, which would make plenty of people on Earth rather anxious.

Still, it's a great theory, and perhaps some day we can get space elevators for cheap transportation into space.

Mars is (relatively) easy. I believe that Kelvar is strong enough for the Martian skyhook. (Gravity makes an incredible difference.)

And the moon would be even easier.

And one could almost certainly build a skyhook that reached down to, say, 30 miles above sea level on Earth. (That's at least twenty miles of cable below the center of gravity, and ? above before it reaches your counterweight.

Then you need your railgun to shoot you high enough to reach the bottom of the skyhook at a fast enough speed to catch it.

Yeah. I 'm convinced. But it would be expensive. I'm convinced that there would be impressive returns, but they would take many years to materialize (and it would depend on pricing issues).

OTOH, Boeing and Lockheed, et. al. would make a bundle while it was being built.
.

We could always just make the string self buoyant (fill air sacks within it with helium or hydrogen).

That only works as far as the string is in atmosphere, a very small percentage of the total length. Buoyancy depends on heavier material surrounding the buoyant object. That's why ocean liners don't fall to the bottom of the ocean, but then again, neither do they hover in the air. Once you're in space, all you've got it gravity.

In college I was able to drive a 1" steel ball through a 12" brick wall with a 3 foot railgun. (Teflon tube with large coils spaced at a semi-logarythmic scale along the length with a simple computer control.) I am sure the steel ball was travelling at mach 1 or more. firing tests over lake michigan would result in a projectile that could not be tracked visually after firing and would not register on a bullet speed detector sold for testing reloads of standard rifle rounds.

if you dont put people in it, I am sure you could get way over mach 3.

I only recieved a C on the project as the instructor could not see any real use for the device or design... typical...

Getting something into orbit isn't about altitude it's about velicoity, specifically overcoming the Earth's escape velocity. You need to be able to shoot something from a point inside the atmosphere up so fast that the pull of the Earth is always less than the current velocity of the craft. At sea level this is about 7 miles per second or 25k miles per hour. A aircraft flying around 20k feet above sea level is only a little bit above sea level compared to the altitude of say the ISS which is about 175 miles or so above sea level right now. So shooting it from a conventional airplane doesn't give you much of a boost since launching it from the ground gives it more time to accelerate.

Launching a rocket horizontally is actually less efficient than launching it vertically because when launched horizontally and having aerofoils to create lift the rocket has to expend some of its burn time building lift to get the craft off the ground. Launching a rocket vertically means it doesn't have to waste precious burn time creating aerodynamic lift.

As an exercise for the poster figure out how much heat would be generated by a craft followed by a ball of air shooting down 32km of pipe accelerating to 2260m/s. Friction is a bitch and would tear the fuck out of anything launched from a big gun like that. One of the caveats of using a railgun to launch stuff is there's only air friction to deal with, not a bunch of mechanical friction which builds up and overwealms your propulsive force. You've also got the explosive force of the air when exiting the tube affecting the trajectory of the craft you just fired. See musket.